The direct analysis of positive blood culture broth using rapid ID/AST systems such as VITEK (bioMerieux, Inc.) has become more widespread as several studies have confirmed the significant benefits of a rapid result. Direct testing from BacT/ALERT FAN bottles (FA, FN or PF) (bioMerieux, Inc.) is complicated by the presence of charcoal particles which make it difficult to prepare a suitable microbial suspension. In particular, the separation of microorganisms from the activated charcoal present in BacT/ALERT FAN bottles has proven to be very difficult due to the broad particle size distribution of the charcoal and the presence of very fine particles not much larger than many microorganisms.
Previous attempts at recovering microorganisms free from adsorbents such as charcoal particles included the use of a polymeric flocculent that agglutinated charcoal particles and resulted in rapid sedimentation. This reagent was however mildly toxic to S. aureus upon prolonged exposure. Furthermore, its optimal concentration was affected by the type of microorganism and whether hemolysis was present in the sample.
Thus, there is a need in the art for a rapid, accurate and inexpensive means for recovering microorganisms from samples wherein the microorganisms are free from particles including adsorbents.